The efferent and afferent connections of the vestibular nuclei in the cat will be studied anatomically using horseradish peroxidase to demonstrate retrograde and anterograde axoplasmic neuronal flow. Having demonstrated the number and location of vestibulo-ocular neurons following relative large injections of peroxidase in the extra-ocular nuclei, an attempt will be made to more precisely locate the vestibulo-ocular neurons which project to the sub-groups of individual eye muscle nuclei. Extremely small injections of horseradish peroxidase will be made into the third and fourth nuclei and the neurons labeled in the vestibular nuclei after retrograde flow of the tracer. Horseradish peroxidase is also being used to demonstrate axons by anterograde filling in order to trace the course and termination of the vestibular nerve in the vestibular nuclei. The transected vestibular nerve in the internal auditory canal will be perfused with peroxidase over a relatively long period of time in order to demonstrate these axons. The ultimate relationships of individual canal fibers with specific eye muscles will be examined.